Here's why:
The Chinese herb ma huang is a member of a primitive family of plants that look like thin, branching, connected straws. A related species, Ephedra nevadensis, grows wild in the American Southwest and is widely called "Mormon tea." However, only the Asian species of ephedra contains the active compounds ephedrine and pseudoephedrine.
Ma huang was traditionally used by Chinese herbalists during the early stages of respiratory infections and also for the short-term treatment of certain kinds of asthma, eczema, hay fever, narcolepsy, and edema.
Japanese chemists isolated ephedrine from ma huang at the turn of the century, and it soon became a primary treatment for asthma in the United States and abroad. Ephedra's other major ingredient, pseudoephedrine, became the decongestant Sudafed.